Sound motion picture apparatus



Dec. 12, 1939. G. B. BANKS 2,183,211

SOUND MOTION PICTURE APPARATUS Filed Dec. 16, 1957 7 1-31 9 161 F K v 161 F 2 I T Jnnentor George Baldwin Ban/i6 V Gttorneg Patented Dec. 12, 1 939 UNITED STATES PATENT oFFicE 2,183,211 SOUND MOTION PICTURE APPARATUS George Baldwin Banks, Chelmsford,England, assignor to Radio Corporation of America, a corporation of, Delaware Application December 16,1937, Serial No. 180,118 In Great BritainFebruary 11, 1937 I 2 Claims. This invention relates to sound heads and amplifier apparatus for use in connectionwith so-called talkie and other sound films, that is to say, to what are generally termed sound heads for sound films. l

The present day practice in connection with .sound head apparatus for talkie and like sound films is to passthe film through a sound head housing in which is a source of light and associated optical system for projecting light through the film, and a photoelectric cell for receiving light modulated in accordance with the sound track on the film. This cell is normally electrically .connected to an externally positioned audio frequency amplifier whereby the sound signals are amplified before utilization, for example,

in a cinematograph .lation. i

There have recently been developed electron discharge devices of the electron multiplier type which are capable of providing large electrical outputs corresponding with varying light inputs; In these devices modulated light is projected theatre loudspeaker instalupon a photoelectric cathode forming part of" the electron multiplier device and the photo-electrons released from this cathode are subjected to electron multiplication (that is to say, are multiplied in number) one or more times by one or a succession of secondary emitter electrodes adapted to produce for a given number of incident primary electrons a larger number, of emitted secondary electrons. Electron multiplier devices of the kind in question, that is to say, of the kind adapted to provide varying electrical outputs in response to a varying light input, present many advantages and may be substituted satisfactorily for the at present more usual sound head photoelectric cell and associated thermionic valve audio frequency amplifier. In practice, however, when it is sought to substitute an elec-. tron multiplier of the kind referred tofor a pho-- to-electric cell and associated amplifier in an existing sound head, there is encountered the serious practical difiiculty that the electron multiplier is somewhat bulkymore especially those known electron multipliers which involve the' the primary object of the invention is to enable sound systems.

existing sound head apparatus to be modified to employ electron multipliers of, the kind referred to, the'said invention may obviously be carried into effect without'starting with an existing sound head apparatus; that is, to say, completely new installations may obviously be made in accordance with thisinvention.

According to this invention, a sound head apparatus for, use in connection witn'sound film comprises within a housing an optical system for providing (as in the usual way) varying light corresponding to sound recorded on a film passed through said housing, and a reflector for reflecting said light through an extension member attached to said housingon to the cathode of an electron multiplier of the kind referred to, said electron multiplier being external with respect to said housing, Preferably the extension member leads into a subsdiary housing containing the electron multiplier, the main housing, the extension and the subsidiary housing being mechan ically connected together soas to constitute one composite housing.

The invention will be described inconnection with the accompanying drawing, in which Figure.

l illustrates one way of carrying out this invention and Figure 2 illustrates the manner in which the invention may be applied to two associated In the manner of carrying out the invention as'illustrated in Figure 1, there is provided withrectangular form an incandescent electric lamp i an image of the filament of which is projected via a condenser lens system 2 on to the sound track portion 3 of a film d which is passed through a gate in said housing as in the usual way; In addition to'the electric lamp and the in a main housing ll of the usual cylindrical or condenser lens system, the housing also houses a projection lens system 42 and a diaphragm member 5 having a narrow slit, the projection lens system 12 and the diaphragm member 5 being arranged, in the order stated, and as in the usual known way, on the side of the remote from the electric lamp so that an image of the sound track is projected on to the narrow slit in the diaphragm member. As so far described, the sound head apparatus is of the at present well-known construction wherein there is usually provided a photo-electric cell on the side of the diaphragm member remote from the light source, this cell being normally carried in a tube inserted through a suitable aperture in one ofjthe side walls of the housing. In accordance with this invention, however, this cell and.

its carrier tube are dispensed with andin place of the cell is fitted a right angled prism 6, the totally reflecting surface of which is arranged to receive light. projected through the diaphragm, member and to reflect it through a right angle out through the normally provided wall aperture for receiving the normal cell tube. Into this aperture is inserted the main housing end M of a tubular extension member l3 along which the reflected light proceeds. Towards the remote end l5 of the extension member [3 is a second right angled prism 3 which again reflects the light through a right angle and thence into a subsidiary housing It mechanically connected with and, if desired, integrally formed with the extension. Across the main housing end [4 of the extension tube is a collimating lens 1, and at or near the mouth of the subsidiary housing 16 is a further lens 9. is such that modulated light, which would normally fall in the usual known arrangements on to a photo-electric cell, is reflected by the first prism 6 and collimated by the collimating lens 7 whose focal length is preferably equal to its optical distance from the projection lens l2. The light is again reflected by the second prism 8 and brought to a focus on the photo-electric cathode (not shown) of the electron multiplier (also not shown but situated in the space generally represented at ID) by the lens 9 in the mouth of the subsidiary housing 16, the focal length of this last-mentioned lens being of course suitably chosen to produce the desired focusing of light.

In a modification, the second prism is dispensed with, and the final lens 9 in the mouth of the subsidiary housing I6 and the said subsidiary housing itself are arranged to be coaxial with the extension tube member i3 so that the light which has entered this tube passes straight down to the cathode of the electron multiplier.

As will be appreciated, in the constructions just described, the extension tube member !3, subsidiary housing !6, first prism 6, collimating lens I, final projection lens 9, and a second prism 8 (if any. may be made as a mechanical unit, the extension tube being arranged to fit into the normally provided photo-electric cell tube aperture in an existing sound head housing ll of standard design.

In come cases, for example in many modern cinematograph theatres, it is customary to employ two associated projector and sound head systems in order to ensure continuity of program, the arrangement being such that one projector and sound head can be started without any interval when the film in the other has come to an end. In such cases it may be desirable, from the point of View of economy or convenience, so to arrange matters that a common electron multiplier may be employed for two sound heads. In such a case, the constructions hereinbefore described may be modified by providing what may be described as a double-ended extension member adapted to fit into two sound head housings one at each end, this double-ended extension leading from either of its ends to a subsidiary housing containing a common electron multiplier. For example, as shown in Figure 2, such a double-ended extension might consist of a straight tube l3! having a branch tube [6| lead-' ing out from the middle of its length after the manner of a T, the branch leading to the subsidiary housing iiil. The ends of the cross bar of the T fit into the normally provided photo-cell tube apertures in the housings Ill and H2 of the two existing sound heads. At the point l5! The whole arrangement where the vertical stroke of the T joins the cross bar is a manually rotatable right angled prism ml which can be moved into either of two positions, one shown in full lines and the other in dotted lines in Figure 2. In one of these positions the prism reflects light projected down one half ofthe cross bar from one sound head into the subsidiary housing, while in its other position the rotatable prism reflects light projected down the other half of the cross bar from the other sound head into the said subsidiary housing. If desired, the lengths of extension tube constituting the cross bar of the T in this construction may be separately hinged, so that either of the two arms which together constitute this said cross bar may be swung out of the way to facilitate reloading of that sound head which is, at any particular time, not in use.

If desired, any of the arrangements hereinbefore described could be modified by arranging a lens system to collimate the light immediately after it had passed the slitted diaphragm. The advantage of collimating the light thus early in the light path is that, in efiect, it reduces the width of the light beam over the rest of the light path and thus enables the prism and lens systems succeeding (in the light path) the collimating lens system in question to be made somewhat smaller than would otherwise (ceteris paribus) be practicable.

Again, if desired, the final lens system preceding the cathode of the electron multiplier may be cylindrical or partially cylindrical so as to give a line image, instead of a spot image, on the said cathode. This is desirable in cases where the electron multiplier has a narrow elongated rectangular photo-electric cathode, since the line image may be arranged to occupy a considerable proportion (practically the whole) of the length of said cathode.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. Photophonographic apparatus comprising two sound heads each provided with a housing, a tubular housing connecting said sound head housings, means in each of said sound heads for directing light beams from said sound heads into said tubular housing, a subsidiary housing connected to said tubular housing and adapted to enclose a photoelectric device, and a reflector in said tubular housing where it is joined by said subsidiary housing, said reflector being rotatable into either of two positions whereby light projectsubsidiary housing, said reflector being rotatable into either of two positions whereby light projected from either one of said sound heads may be selectively directed into said subsidiary housing.

GEORGE BALDWIN BANKS. 

